This invention relates to activated carbon. In addition, this invention relates to shaped activated carbon formed from powdered activated carbon. This invention also relates to shaped activated carbon formed from powdered activated carbon and a binder material.
Activated carbons are extensively used to purify, decolorize, deodorize, dechlorinate, and detoxicate potable waters; for solvent recovery and air purification in inhabited spaces such as restaurants, food-processing, and chemical industries; in the purification of many chemical and foodstuff products; and in a variety of gas phase applications. Activated carbons are of interest in many economic sectors and concern industries as diverse as food processing, pharmaceuticals, chemical, petroleum, mining, nuclear, automobile, and vacuum manufacturing. In particular, characterization of the carbon surface and its porous structure with respect to the chemical composition of the surface, pore size distribution, and surface area is of vital importance whenever quantitative data for processes occurring or starting at the surface of the carbon, such as surface reactions, adsorption, degassing, and surface treatment, are required.
Shaped carbon bodies are generally produced from powdered carbon particles with organic or inorganic binders. Carbon powder, binder, water, and other ingredients are mixed to form a material that is subsequently shaped. The shaped bodies of wet carbon/binder mixture must be thermally treated at high temperatures to increase product strength and water stability. For example, the prior art teaches using clay and phenolic resin polymer as binders. In particular, U.S. Pat. No. 4,677,086 to McCue et al. first disclosed the use of bentonite clay as a binder for powdered carbon, which disclosure is incorporated herein by reference. Subsequent improvements on this technology are disclosed in U.S. Pat. Nos. 5,204,310, 5,206,207, 5,238,470, 5,250,491, 5,276,000, 5,304,527, 5,538,932, 5,691,270, 5,736,481, 5,736,485, and 5,863,858, all assigned to Westvaco Corporation (hereafter, xe2x80x9cthe Westvaco patentsxe2x80x9d), the disclosures of which are incorporated herein by reference.
This prior art binder technology requires expensive plant equipment, is encumbered with a costly high temperature heat treatment step, and results in products which may fail to meet all required property characteristics for certain desired applications.
Also, other activated carbon binder technology includes U.S. Pat. No. 5,389,325 to Bookbinder et al., which describes activated carbon bodies having phenolic resin binder and describes a method to manufacture an extruded honeycomb that is water-resistant. Activated carbon powder was mixed with 5-35% phenolic resin and 4-10% organic plasticizer as an extrusion aid. The plasticizer was selected from a variety of cellulose derivatives. Thus, Bookbinder et al. teach inclusion of cellulose derivatives only as an extrusion aid in conjunction with phenolic resin as the binder material.
U.S. Pat. No. 4,866,023 to Ritter et al. discloses a process for the shaping agglomeration of particulate solids and solids produced by the process. The patentees claim a two-step process to granulate solid powders such as metal powders, insoluble metal salts, and activated carbons. Solid powders were first mixed with a polymeric binder and water to form a viscid mass that was shaped into droplets. The droplets were immediately immersed in a solution, which contained polyvalent cations such as Ca2+, Fe3+, Cu2+, etc. Water stability was obtained when the metal cations reacted with the polymer binder to form water-insoluble salts.
U.S. Pat. No. 4,920,090 to Ritter et al. discloses a process for the formation of shaped agglomerates from particulate solids and claims a binder system that improves the product thermal stability over U.S. Pat. No. 4,866,023. The previous cellulosic binder was replaced with polymers containing anhydrides of dicarboxylic acid. Metal cations were replaced with anhydride-reactivated polyamines. The same two-step manufacturing process was used.
In each case, the water stability of the prior art shaped carbon body was obtained by insolubilizing the polymer binders without a high-temperature treatment. Additionally, binders, crosslinking agents, or manufacturing processes were used other than as employed in the invention herein disclosed.
Finally, U.S. Pat. No. 4,215,096 to Sinha et al. teaches impregnating activated carbon with sodium hydroxide (NaOH) for use in purification of gas streams contaminated with acid and acid precursor gases and vapors.